Use the top-level ratio 8:3 to find how many adults and seniors there are, then break each group down using sub-ratios.
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• Top-level ratio 8:3 means 11 units in total.
• 110 ÷ 11 = 10 per unit.
• Adults: 8 × 10 = 80
• Seniors: 3 × 10 = 30
For the adults (sub-ratio 3 + 1):
• 4 parts = 20 per part
• bought snacks: 3 × 20 = 60
• didn't: 1 × 20 = 20
For the seniors (sub-ratio 1 + 2):
• 3 parts = 10 per part
• bought snacks: 1 × 10 = 10
• didn't: 2 × 10 = 20
Total bought snacks: 60 + 10 = 70.
Check: 80 + 30 = 110 = total (110). ✓
Final Answer: 70